Britney -

*Dammar*

Dammar has been used as a varnish for paintings since the nineteenth
century, and still is used today by conservators.  Dammar and mastic,
another natural tree resin, saturate paint surfaces even when applied as a
very thin layer.  Chemical changes that occur with age cause these resins to
yellow and become less soluble.  Future removal might require the use of
solvents that could damage some oil paints.  For these reasons, conservators
usually apply these resins in very thin films, often attempt to slow the
chemical changes by adding various compounds, or choose one of several
synthetic resin alternatives.

The recommendation to use a matte varnish suggests that a glossy, saturating
varnish such as dammar is not appropriate for the mural.  Given this, you
may want to ask the conservator about synthetic alternatives that are less
glossy and less prone to yellowing.  The future cost to remove a yellowed
varnish from the mural is another consideration.

*Isolating varnish*

Conservators often use varnish to separate touch ups (restoration) from the
original paint surface.  In theory, this isolating varnish remains soluble
in solvents that do not damage the paint.  For the reasons given in the
preceding section, dammar and mastic are not appropriate for all types of
paint.  Ask the conservator about synthetic alternatives.

*Odorless paint thinner*

Odorless paint thinner is a solvent and diluent (thinner) for many natural
and synthetic resins, including fresh oil paint.  The suggestion to use an
odorless paint thinner over the murals, probably is intended to remove oily
grime preceding varnish application.  Grime removal is recommended prior to
varnish application for several reasons: (1) grime can affect color balance,
clarity, and contrast of the image, (2) second, grime can prevent varnish
from wetting and "sticking to" the paint surface, and (3) grime can promote
chemical degradation of the varnish.  Ask the conservator to confirm this
purpose and specify that a paint thinner be used that has no or low residual
solids.

Good luck.

James Martin, Fellow AIC
Orion Analytical, LLC
Post Office Box 550
Williamstown, MA 01267
tel: 413-458-0233
fax: 413-458-5542
[log in to unmask]
www.orionanalytical.com


Date:    Mon, 12 Feb 2001 12:17:32 -0500
From:    Britney <[log in to unmask]>
Subject: cleaning a mural

I have a question.  I'm not much of an art person so any info will be
helpful. We are in the middle of a diorama renovation.  We had a company
come out, view the dioramas and give us recommendations on new exhibit
designs.  One of their recommendations was to use "De Mar Varnish (matte)
to coat our oil painting murals so that we can make touch ups on it without
damaging the original mural.  Another suggestion they had was to use an
odorless paint thinner over the murals.  Has anyone used these materials or
know anything about this product specifically.

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